An image display apparatus has been distributed in which a combined image where a virtual object image is superimposed onto an image photographed by a camera (photographed image) is displayed to a display unit to provide a viewer of the display unit with an augmented reality. As for such an apparatus, a device has been known that uses a head-mounted display (HMD) having a camera attached thereto (see, for example, Patent Literature 1).
Patent Literature 1 discloses a system that provides a viewer who wears an HMD having a camera as well as a third party who watches a stationary type display separately provided from the HMD with an augmented reality by the HMD and the display. The system displays a combined image in which a virtual object image is superimposed onto an image photographed by a camera provided on the HMD, transmits the combined image to an external display, and causes the combined image to be displayed on the external display.
In such a system, the viewer who wears the HMD may watch an image that responds to the movement of his head. Therefore, even when an image displayed on the HMD shakes or is tilted, the viewer may not feel a sense of discomfort.
However, since a third party who sees the same image through the display may feel that the image is being changed regardless of his intention, there is a likelihood of causing the third party to feel an image motion sickness. Accordingly, in this system, when a slope is present in an image displayed on the HMD, the slope of the image to be displayed on the display is corrected to provide an image that does not cause a sense of discomfort to a third party.
Also, Patent Literature 2 discloses a method in which a motion vector is calculated from an input image and an image to be output externally is held when either size or direction of the motion vector is large in order to reduce an image motion sickness.